hey...im new to posintg on this message board...i have a 1990 firebird formula with a stock 305 TBI except for open element with k&n filteri just took my car to inspection in NJ...the max allowed nitrates is 1277 and mine is 2784...i also get horrible gas mileage...200 miles to the tank...i have new plugs wires cap and rotor...just changed timing chain....i bought the car last year and dont know if the cat was changed or not...so im thinking that or something in the EGR but im not getting any error codes...also im running fairly rich..i get some black smoke at high rpms..not alot...just want someone elses opinion

 

Sounds like you know what the problems are. I'd suggest replacing the oyxgen sensor, since it's likely never been replaced. The cat probably needs to be replaced as well. EGR could be clogged or unplugged, or just not working. I'd check to see if anyone has fooled around with the fuel pressure, or if you've got an aftermarket chip in there that could cause you to run rich.

 

hey thanks alot...i dont think i have an after market chip but im not expierenced on them just yet...im only 17...still learning...havent even looked for one...where do i look? does it plug into the ECM? i also have the open element...would that make me run richer? i thought it could be that it hasnt had a tune up in a long time...i have all the stuff, havent gotten to it yet...hopefully by the weekend ill get it done...next project is the cat if this tune up doesnt do anything for me...and yeah i have no idea when this the cat or o2 were replaced, dont even know when the last tune up was

 

Yeah, it plugs into the ecm. You just need to take the panel off over the carpet on the passenger side foot area. Any aftermarket chip will probably lower your gas mileage and raise your NOx.

As far as mileage and emissions, that tune up should definitely help. Try to get someone to pretest your car before you do the real test next time. You might want to take a trip over to the TBI board and see if those guys have any tips for passing emissions and getting better gas mileage. Don't forget that O2 sensor. Good luck.

 

i got the 305 tbi also. if the exhaust gases smell like sulfer aka rotting eggs, it means the cat is bad. mines like that and i didnt want to pass nj emissions

 

nah it doesnt smell like sulfer or rotten eggs id definetly notice that...sometimes...veyr rarely i smell a burning plastic smell...but never any smoke from under the hood and nothings burning or melting under the hood that i can see from the top or bottom....and as far as the smell...it smells like any exhaust...it does smell a bit rich though as well...but im like 95% sure im runnin pretty rich though so...yeah...thanks for all your help guys

 

Sherlock Holmes once said: the simpliest scenario that meets all of the facts is usually the correct one....

High NOx is caused by a high combustion chamber temperature. This is alieviated by the EGR system. By putting exhaust gasses in the intake charge you actually make the fuel burn slower and less effectively thereby making less heat in the cumbustion chamber. I would check the operation of the EGR with a vaccuum pump, and check all of the vaccuum lines etc....

High NOx can also be caused by excessive advanced timing, in your first post you state that it had a timing chain replaced, and a new cap rotor and wires, The distributor was more than likely moved at some point during that repair. I would check the timing to make sure it is set properly.

From my experience Hydrocarbons and CO are usually high when O2 sensors go bad, how did the car fare in regards to those numbers?

Best of luck , and welcome to the boards.....

Bagz

 

i just replaced the timing chain...i havent done the cap or rotor yet...im doin the cap rotor plugs and wires friday....and the car runs beautifully...engine is niec and strong and smooth....but my NOx is way over twice the legal limit and my mpg are terrible...i dont have any misses or sputtering or surging or anything...im really confused...after my tune up perhaps i will look more into the EGR being clogged or something...my HC and CO were ok...

HC legal limit is 162 and mine was 143
CO legal limit is 0.91 and mine was 0.57

and also...could someone explain the difference between combustion chamber temp and like engine temperature? does the engine temp even have anything to do with combustion chamber temp? i think i know but im not sure...also...car parts (auto store around here) said that a bottle of that sure-pass stuff wouldnt help me since my NOx is so high, anyone have experience with that sure pass stuff?

 

Combustion chamber temp is the temperature of the air in the chamber when the spark plug fires. If that air is too hot the fuel air mix burns at a rate that produces NOx. if it gets even hotter you get detonation (pinging) The EGR system introduces exhaust gas into the intake charge to slow the burn down. The slower the burn the cooler the combustion chamber temp gets lower NOX.....

Since you pass on HC and CO the engine is not running too rich. You say the engine runs smooth and strong im willing to bet the initial timing is way advanced. the high advance can also contribute to high temps, check the timing when you do the cap and rotor etc......

The poor gas mileage is probaly caused by the bad timing, engine is running so advanced it is not making optimum power....

Engine coolant temp (gauge in car) if too hot can contribute to high Combustion chamber temp, but they are not the same....

 

alright im gonna have to check out the cap and rotor...i was gonna hold off on the tune up stuff for a little due to some research i found on the air divertor valve sending air into the exhaust manifold makin it run right and a whole bunch of stuff that i dont feel like explaining...but yeah...more on the timing...how do i tell if its advanced...mine is computer controlled and i was always told that even if you advance the timing, the computer will automatically retard it...is the only way to tell if its advanced by using a timing light? dont know very much about timing either...still learning....alot

 

Yes the computer controls the timing, but the base line needs to be set so the ECM knows where its starting from. Check a chiltons, haynes manual or the emissions sticker on how to check the timing. Ususlly you disconnect teh 4 pin plug from teh distributor and set teh timing so that the timing mark is at zero. You need a timimg light to make the adjustment.

 

alright im definetly gonna have to check that out...but as i said...i replaced the timing chain, which involves taking the crank pulley off and the vibration damper...i might be wrong, but i thought the timing light lit up a mark on one of those when the spark plug went off (this is to my understanding, nbever checked timing before, correct me if im wrong), and i removed those when i did the chain and dont know if they went back on the same way they came off...i havent looked in my manual yet...so...yeah i guess thats it thanks guys for all the input

 

The damper is where you get the timing reading. It only goes on one way. If you think back youll remeber a slot in the balancer and a ridge on the crank. As far as you nox it can be caused by a couple other things not mentioned. One being timing to far retarded and the other being a mixture that is to lean. First thing id check/replace is the egr.